Hey guys, this isn’t a motor driver I know (tried to find an off topic section…) but it’s for controlling a fan speed. I had some pcbs made with the schematic shown. They don’t work as they are, and I tried a couple variations by modifying the pcb, and can’t get the drivers to do anything. I tried connecting VCC to 5 volts instead of 12. Tried adding higher capacitance capacitor to the bootstrap capacitor section.
The voltage on the VB pin, which iirc is supposed to be higher than the high voltage the mosfet is switching, is always the same as VCC. I tried connecting SD (shutdown) pin to 5 volts, too. It never does anything. I make the in pin high or low, just doesn’t do anything useful? I tried removing the 4.7 ohm resistor at the gate of the mosfet too, no dice. I don’t see anything helpful in the datasheet
The datasheet is not clear at all, but I think connecting that shutdown pin to ground will disable the chip. But if you already tried connecting it to 5V, then there must be some other problem as well.
:(. yeah. I didn’t think it would be this hard. I tried both, it still does nothing useful. I checked all connections, everything seems to be good. Tried a fresh board in case I fried it during previous experimentation. It never does anything but sit there?
If I can’t figure this out I’ll have to go to a small bipolar transistor to drive the mosfet and just use it as a low side switch instead, or maybe use a different driver I guess. I should have used the fortior one that was proven to work on other boards.
Could it be the mosfets got fried by too high gate voltage? Assuming this is the correct datasheet https://toshiba.semicon-storage.com/info/RFM04U6P_datasheet_en_20140301.pdf?did=1927&prodName=RFM04U6P and that “gain-source voltage” is a typo, it says absolute max 3V. It looks like you’re applying 12V to the gate.
P.S. The Fortior driver is good, but don’t be afraid to use DRV8300 either. It turned out my struggle with it was due to a bad batch of SE3082G mosfets.
Hm, wait no the source should be at high potential, when it is driving the load the drain, pin 3, is at 12 volts, and the other side, pin 2, the source, should be at very close to 12 volts. Because most of the voltage drop should occur through the load. In the case of the resistor and led, for instance, for now.
The job of the driver is to constantly keep the gate of the transistor at 3 volts higher than the source, or something, to keep it conducting. This is partly why we need the driver, it needs to create a voltage that’s actually higher than the supply voltage. If the impedance of the load varies for some reason, the driver must have to react fast to keep the mosfet conducting while not driving the gate too hard at other times.
